摘要:

The neutral particle analyzer with energy and mass selection capability built for JET is described. The analyzer is able to detect in the same shot both H atoms from 0.3 to 320 keV and D atoms from 0.15 to 160 keV. In order to optimize the ion optics of the analyzer an oblique entrance in the magnet has been chosen. An ion trajectory code shows that in this way a good mass separation and a high efficiency can be achieved. The problems inherent in the analyzer calibration for a wide energy range are discussed, and the calibration procedure is described. In conclusion, the calibration results obtained with five analyzers are presented, together with theoretical consideration on ion optics and atomic processes, which have enabled us to write a simple interpolation formula for the experimental data.

ISSN:0034-6748    

DOI:10.1063/1.1139634

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Tests of a 300‐keV electrostatic electron beam injector with a magnetic crowbar switch are described. The saturable ferrite core switch allows generation of a constant voltage, 80‐ns pulse directly from a Marx generator. Inductive isolation in the switch permits direct access to the high‐voltage electrode for thermionic or active plasma cathode experiments. The pulse modulator can drive a 1.5‐kA load. A high brightness 290‐A beam from a felt plasma‐emission cathode was extracted and propagated in vacuum. Because of the reliability of the magnetic crowbar switch, more than 500 shots were accumulated on the cathode at over 1 kA/cm2with no degradation of the output. The output beam had a normalized brightness of 2.6×108A/(m rad)2. A solenoidal lens was used to match the space‐charge‐dominated beam into a 1‐m‐long periodic focusing system with 25 reversing solenoidal coils. A beam current of 150 A was successfully transported through the 1.7‐cm radius tube.

ISSN:0034-6748    

DOI:10.1063/1.1139635

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A method of triggering multichannel rail‐gap switches is described. The method involves producing a glow discharge between a strip of semiconductor material and one of the rail‐gap electrodes, the trigger discharge is arranged to extend to the full length of the rail electrode. This trigger technique has been used to trigger a small rail‐gap switch and has been shown to be capable of producing high arc densities in the switch. It is expected that the trigger will be suitable for use with long lifetime rail‐gap switches.

ISSN:0034-6748    

DOI:10.1063/1.1139667

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We describe a valve for production of jet‐cooled species in a pulsed, long‐path‐length (1.2‐cm) supersonic expansion. The valve produces 150–600‐&mgr;s‐duration pulses at repetition rates up to 60 Hz from a nozzle with variable slit width, and is suitable for use with corrosive gases and vapors.

ISSN:0034-6748    

DOI:10.1063/1.1139636

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A molecular beam source incorporating a dc discharge is used to study the emission spectrum of helium excimers near 600 A˚ and of argon excimers near 1070 A˚. It is shown that under certain conditions the strength of the excimer radiation approaches that due to the helium resonance lines. The new source is expected to be useful for studying other excimers in the vacuum ultraviolet region of the spectrum.

ISSN:0034-6748    

DOI:10.1063/1.1139637

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A manually operated Burnett apparatus has been converted into a semiautomated Burnett–isochoric PVT facility. An automated pressure injector with dedicated control logic nulls a sensitive differential pressure indicator. A microcomputer is used in setting the control temperature, monitoring equilibration, measuring temperature and pressure, processing the raw data, and storing the information. The quality of the apparatus is demonstrated by means of a low‐density and a high‐density isochore obtained for a geothermal working fluid mixture in one‐phase, two‐phase, and supercritical regimes, including a dew and a bubble point.

ISSN:0034-6748    

DOI:10.1063/1.1139638

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We describe an instrument consisting of two adjacent Langmuir troughs and an apparatus capable of dipping substrates in either trough. Such a capability permits the fabrication of Langmuir–Blodgett multilayer films consisting of two alternating components. The troughs are housed in a hermetically sealed enclosure which may be evacuated to permit the establishment of a clean and/or modified (e.g., O2free) atmosphere. The enclosure is double walled for circulation of thermostating fluid (e.g., ethylene glycol) in order to establish temperatures in the range −30 to 130 °C. The monolayer pressures, film size, and dipping sequence can be controlled manually or by a computer. The surface pressure in each trough is sensed by independent Cahn balances employing filter paper ‘‘Wilhelmy plates’’ in such a manner as to maintain the hermetic seal.

ISSN:0034-6748    

DOI:10.1063/1.1139639

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The Graduate Center for Cloud Physics Research at UMR has developed a cloud simulation facility to study phenomena occurring in terrestrial clouds and fogs. The facility consists of a pair of precision cooled‐wall expansion chambers along with extensive supporting equipment. The smaller of these chambers, described in this article, is fully operational, and is capable of simulating a broad range of in‐cloud thermodynamic conditions. It is currently being used to study water drop growth and evaporation for drops nucleated (activated) on well‐characterized aerosol particles. Measurements have been made not only for continuous expansions (simulated updraft) but also for cyclic conditions, i.e., sequences of expansion‐compression cycles resulting in alternating drop growth and evaporation. The larger of the two cloud chambers is nearing completion and will provide a broader range of conditions than the smaller chamber. The facility is supported by a fully implemented aerosol laboratory which routinely produces well‐characterized condensation nuclei. The aerosol laboratory contains extensive instrumentation designed to both shape and measure the size distribution and nucleating characteristics of the generated aerosol. The cloud simulation facility also includes a humidifier to bring an air sample to a known humidity before it is put into the cloud chamber. A systematic program to infer effective condensation coefficients (of water vapor on cloud drop) under a variety of well‐controlled simulated in‐cloud conditions is now under way. Analysis of current experiments with standard drop growth theory indicates a variation of condensation coefficient with observation time, with values sufficiently low to explain one of the current mysteries in cloud physics:viz., the broad spread of drop sizes observed in natural clouds. This article includes a description and performance specifications of the smaller cloud simulation chamber.

ISSN:0034-6748    

DOI:10.1063/1.1139640

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The directional sensitivity of unplated slanted‐wire probes is experimentally investigated. It is shown that the yaw response of these probes depends on the roll angle, &bgr;, at which the plane formed by the wire and the prongs is oriented with respect to the yaw plane. At &bgr;=0°, when both planes are aligned with each other, the constant velocity characteristics are monotonic functions of the yaw angle, &psgr;, implying a unique correspondence between the output signals and flow direction. When the two planes are not aligned with each other, a region of yaw angles is found within which the hot‐wire signals become nonuniquely related to the yaw orientation of the probe. The size of this region is shown to depend on the particular value of &bgr;; it increases with increasing &bgr; and vice versa. Problems of nonuniqueness are also found during calibrations of two‐ and three‐wire probes. It is shown that such problems result either from improper orientation of the wires with respect to the calibration plane (in the case of an X probe) or from the arrangement of the wires on the probe (in the case of a three‐wire probe) or both. To avoid nonuniqueness and ambiguous results, the use of these probes is restricted to an experimentally determined range of angular directions of the flow. However, from the current findings it appears that, in the case of a conventional three‐wire probe, the limiting values of the flow angles (angular directions) are relatively small. It is concluded, therefore, that for measurements in three‐dimensional or highly turbulent flows (in which the instantaneous angular directions of the flow are relatively large), an entirely new arrangement of the wires on the probe should be sought.

ISSN:0034-6748    

DOI:10.1063/1.1139641

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Three related waveguide devices are described for measuring the dielectric constants of fibers and rods. In each device the sample is located one‐quarter guide wavelength from the shorted end of the waveguide. A slot in the side or end of the guide permits easy insertion and removal of a fiber sample without having to thread it through holes in the waveguide. The dielectric constant along the length of the fibers can be measured as they are rapidly pulled through the device. The technique allows accurate measurement of samples having a wide range of diameters and dielectric constants. Measurements of carbon, nickel alloy, and alumina samples are described, and the experimental sources of error are analyzed.

ISSN:0034-6748    

DOI:10.1063/1.1139642

出版商:AIP    

年代:1987

数据来源: AIP